Frequency discriminator network



L. BRCK FREQUENCY- DISCRIHINATOR NETWORK Filed May 16 1939 INV EN TOR. L0 'R BRUC( ,www

ATTORNEY.

QQK NESS spsn 10,1940.

Patented Sept. 10, 1940 einen FREQUENCY DISCRIMINATOR NETWORK Lothar Brck, Berlin, Germany, assignor to Telefunken Gesellschaft fiir` Drahtlose Telegraphie m. b. H., Berlin, Germany, a corporation of Germany Application May 16, 1939, Serial No. 273,898 In Germany June 15, 1938 Claims.

A receiver is known in the prior art comprising means adapted to convert a frequency departure of the incoming intermediate frequency v(I. F.) signals from its rated, or nominal, Value into a 5 direct current voltage proportional to or characterizing the frequency departure or deviation. In this arrangement the incoming alternating potential is multiplicatively mixed with another alternating potential of the same frequency, the latter presenting a phase angle of exactly 90 degrees only in the absence of a frequency departure. This mixing is eiiected by impressing each potential to a distinct control grid separated from each other by a screen grid in a multi-grid type of tube. The regulator direct current potential is taken oiT at the plate. Now, this arrangement offers the advantage over other arrangements known in the prior art in which the phase-dis placed oscillations are superposed upon each 20 other and are rectified (additive mixing) in that the regulator potential, When the tuned state has been reached, independently and regardless of the amplitude of the incoming oscillation, has the same value, namely the value which it also 25 assumes when there is no alternating potential atall. Hence, contradistinct from the arrangements known in the art involving additive mixing, no push-pull scheme is required in the arrangement referred to at the outset and involving 30 multiplicative mixing.

According to the present invention, the arrangement known in the art is improved insofar as the operating conditions of the tube are so chosen that, in the absence of an alternating po-v 35 tential the plate direct current potential and the screen grid direct current potential are of the same value, and that the regulator potential consists of ythe difference between the plate direct current voltage and the screen grid direct cur- 49 rent voltage.

Quite apart from the fact that in this way a compensation of the quiescent (feed) value of the plate direct current potential is secured in a positive manner, the chief merit of the invention is 45 that the regulation gradient is augmented. For,

since the control grid closest to the cathode controls the screen grid current and the plate current in phase, while the second control grid causes distribution control action upon the screen ,-30 grid and the plate so that the screen grid current and the plate current are controlled in phase opposition, it follows that in the presence of an incoming (signal) alternating potential having a frequency deviating from the rated or nominal 55 frequency the plate direct current voltage and (Cl. Z50-40) the screen grid direct current potential vary in opposite directions. Thus, for instance, if the plate direct current voltage rises, the screen grid direct current potential decreases.

A particular advantage of the invention may *5, be taken to reside in the fact that the regulator potential is lesssensitiva or responsive, to fluctuations in the emission of the tube and also to Variations in the operating potential. For it will be seen that, if the electron emissivity of a tube decreases as a result of prolonged use, the plate direct current voltage will rise because of the decrease in the plate current. In the arrangement of the prior art above referred to, this would mean that the regulator potential, upon the correct tuning having been attained, no longer has the value which it had at the time the receiver started to operate. However, in the present arrangement the screen grid potential also rises so that the regulator direct current voltage here taken ofi, upon the occurrence of emissivity changes in the tube, will vary not at all or only to a substantially lesser degree. If the working conditions are properly chosen, in other words if the load resistances of the screen y grid and the plate as well as the potentials impressed upon these resistances are correctly chosen, then conditions may be made so that, in the presence of accurate tuning, the regulator potential will, within wide limits, be independent I both of the amplitude of the incoming oscillation as well as independent of the emission of the multi-grid tube.

An embodiment of the invention is shown in the drawings which is a circuit' diagram of a 35 heterodyne type receiver. The signal oscillation is amplified in the receiver section H, changed into a iixed I. F. (intermediate frequency) bybeat action with a locally generated oscillation, and then again amplified, and the I. F. energy is fed f40 to the bandpass iilter comprising the two oscillation circuits K1 and K2 tuned to the nominal or rated value of the I. F. .The alternating p0- tential which arises at the secondary circuit K2 is'directly impressed upon the grid G1 of am- 45 plifier tube V directly adjacent to the cathode, while the alternating potential arising at the primary circuit K1 is impressed upon the second control grid G2 by way of the coupling condenser C. The two control grids are separated from each other by a vscreen grid S1, the latter being capacitively grounded by the condenser C1, and f being connected with the positive pole of the plate potential source by way oi an ohmic load resistance R1. Between the second control grid y515 G2 and the plate A is another screen grid Sz. The plate lead contains another circuit K3 which is tuned to th-e I. F., the said circuit Ks transferring by way of a similar circuit K4 the I. F. oscillation to the network N. The latter, for instance, may comprise a signal diode detector as well as an audio (A. F.) amplifier. Associated with the output circuit of the latter is the loudspeaker L. The end of the plate coil whichy is not associated with the plate A is grounded by way of the condenser C2, and connected by way of the resistance R2 with the positive pole of the potential source.

Resistances R1 and R2 are so adjusted that in the absence of signal alternating potential the direct current voltages of the plate A and the screen grid S1 are exactly of the same value.A

This condition is obtained if the resistances are inversely proportional to the direct current taken by the screen grid and the plate. In this manner conditions can be made so that inside limits of fluctuation of the emission of tube V which are not unduly great (and of uctuations of the working potentials) the equality of the plate direct current voltage and the screen grid direct current voltage is preserved.

The control grid biasing potentials of the tube are so chosen that also in the presence of the highest alternating potential amplitude arising at the grids, the grid swing substantially will keep inside the straight portion of the characteristic. For this purpose the receiver is suitably provided with automatic volume control means. Of course, as will be understood, tube V should not be subject to amplitude regulation, in fact, the regulator action must be brought upon the input' tubes in such a way that the oscillation amplitude at the band-pass filter K1 and K2 will be practically constant for all transmitters.

The diierence between the screen grid direct current voltage and the plate direct current voltage is equal to Zero both in the absence of a signal oscillation as well as when the frequency of the signal ocillatio-n is equal to the correct I. F. In case of detuning, the regulator potential is either positive or negative according to the detuning. In the embodiment shown in the drawings, this regulator potential is used for tuning indication.

What is used for this purpose is a cathode ray tube comprising a cathode K, a positively biased accelerator (gun) and diaphragm electrode B, two deflector electrodes A1 and A2, and a luminescent screen S. The electron beam from cathode K forms a luminous spot on screen S. Upon the deflector electrode A1 is impressed the screen grid direct current potential, while upon the deflector electrode A2 is impressed the plate direct current potential taken off at the junction of circuit K3 and the resistance R2. In the presence of proper tuning, the indicator spot will be situated exactly in the center of the screen, regardless of the amplitude of the incoming wave. In the case of detuning, it will be displaced either way; that is, to the right or t'o the left-hand side of the center. If valuesv are chosen as above prescribed, the zero position will not change, even in case of changes in emission of the amplifier tube V and in the operating po-tentials.

The second screen grid S2, under certain circumstances, may be dispensed with. .In other words, a pentode may be employed in lieu of ay hexode. However, if desired, the regulator potential could be taken off also between the two screen grids of the hexode, with the result that so far as the regulating potential is concerned, the second screen grid would play the part of the plate, while the plate properly so-called serves in this instance only for the output and delivery of the I. F. potential. Instead of being impressed with the whole primary potential of the bandpass filters K1, vK2, the control grid Gzcould be impressed only with a part thereof, and this would mean a moreeiiicient utilization of the filter action of the bandpass lter. Finally, as will be seen, the two control grid connections and terminals could be exchanged.

What is' claimed is:

1. In combination with an electron discharge tube having an electron emission element, a positive cold electrode spaced therefrom, a pair of 1 control electrodes between the emission element` and the cold electrode, and a second positive cold electrode between the pair of control electrodes, at least two cascaded high frequency signal crcuits tuned to a common assigned frequency value, means for applying signal energy to the rst of the cascaded circuits, means coupling each of the control electrodes to a given one of said cascaded circuits, a resistive impedance connected in circuit with each one of said positive cold electrodes, said impedances having relative values such that the voltages of the cold electrodes are substantially equal in the absence of applied signal energy, and means for deriving unidirectional voltages developed across the irnpedances.

2. In combination with an electron discharge tube having an electron emission element, a positive cold .electrode spaced therefrom, a pair of control electrodes between the emission element and the cold electrode, and a second positive cold electrode between the pair of control electrodes, at least two cascaded high frequency signal circuits tuned to a common assigned frequency value, means for applying signal energy to the first of the cascaded circuits, means coupling each of the control electrodes to a given one of said cascaded circuits, a resistive impedance connected in circuit with each one of said positive cold electrodes, said impedances having relative values such that the voltages of the cold electrodes are substantially equal in the absence of applied signal energy, and means for deriving unidirectional voltages developed ac-ross the impedances, said deriving means including a visual indicator having connections to said impedances,

ytube having an electron emission element, a positive cold electrode spaced therefrom, a pair of control electrodes between the emission element and the cold electrode, and a second positive cold electrode between the pair of control electrodes, at least two cascaded high frequency signal circuits tuned to a common assigned frequency value, means for applying signal energy to the first of the cascaded circuits, means coupling each of the control electrodes to a given one of said cascaded circuits, a resistive impedance connected in circuit with each one of said positive cold electrodes, said impedances having relative values such that the voltages of the cold electrodes are substantially equal'in the absence of applied signal energy, and means for deriving unidirectional voltages developed across the impedances, a common source of positive potential for said cold electrodes, and both said impedances being connected to said common source.

4. In combination with an electron discharge tube having an electron emission element, a positive cold electrode spaced therefrom, a pair of `control electrodes between the emission element and the cold electrode, and a, second positive cold electrode between the pair of control electrodes, at least two cascaded high frequency signal circuits tuned to a common assigned frequency value, means for applying signal energy to the first of the cascaded circuits, means coupling each of the control electrodes to a given one of said cascaded circuits, a resistive impedance connected in circ uit With each one of said positive cold electrodes,

, said impedances having relative values such that the voltages of the cold electrodes are substantially equal in the absence of applied signal energy, and means for deriving unidirectional voltages developed across the impedances, means for biasing said control electrodes negative, said first cold electrode being a plate electrode, and a resonant signal output circuit connected in circuit with the 20 plate.

5. In combination with a source of signal energy Whose frequency varies with respect to an assigned frequency value, a network for derivinga variable-amplitude unidirectional voltage from saidv signal energy, said network comprising an electron discharge tube having at least a cathode, control grid, positive screen grid, second control grid and output electrode arranged in the order named, independent resistors in circuit with said screen grid and output electrode, means for connecting said resistors to a source of positive voltage, means coupling said signal source to said control grids so that the signals are applied thereto in phase quadrature, and said resistors being so related in valuethat the screen grid and output electrode voltages are equal When the signal frequency equals said assigned Value.

LOTHAR BRCK. 

